This invention relates to a loop transmission system (which may be referred to as a data highway) having a loop transmission path and a plurality of stations (node processors) connected to the loop to carry out data transmission among the stations, and more particularly, to a loop transmission system which can easily confirm whether a transmission frame sent out from a sending station has been correctly received by a receiving station in the data transmission between the stations.
Conventionally, in order to confirm at the sending station (referred to as S-ST hereinafter) that a transmission frame sent out from the S-ST has been correctly received by the receiving station (referred to as R-ST hereinafter (it has been proposed to generate a response frame at the R-ST side to show whether the frame has been correctly received or not and to send this response frame out to the S-ST side so that the S-ST side can confirm, upon receiving this response frame, whether or not the transmission frame has been received by the R-ST.
This conventional system, however, has the following drawbacks.
(1) The R-ST side is burdened with considerable work for preparing a response frame, which may reduce the processing capacity of the R-ST side. PA0 (2) Since respective response frames sent out from the R-ST's are usually not in the order received by the S-ST side (i.e. the response frames are not necessarily received in the order in which the corresponding transmission frames have been sent out from the S-ST's), the confirmation processing of the response frames at the S-ST side becomes complex.